Why are RJ45's wired with pair 2 straddling pair 3? I think it's a throw back to old telephone cabling but it still doesn't make sense!
1 comment:
Anonymous
said...
Well, throw back is probably not the best term, I would put it as "backwards compatibility". Basically, the two famous structured cabling pin layouts ( T568A and T568B ) co-exist because they have two opposite goals in mind. T568A is designed to accommodate a 2-pair phone. Here pairs 1 and 2 are in USOC layout so an old 2-line phone works right away if plugged into such jack. On the other hand T568B is designed to prevent damage to digital phones and, later, Ethernet equipment if accidentally plugged into an analog phone jack (pair 1 disabled and 2 and 3 are used instead)
1 comment:
Well, throw back is probably not the best term, I would put it as "backwards compatibility". Basically, the two famous structured cabling pin layouts ( T568A and T568B ) co-exist because they have two opposite goals in mind. T568A is designed to accommodate a 2-pair phone. Here pairs 1 and 2 are in USOC layout so an old 2-line phone works right away if plugged into such jack. On the other hand T568B is designed to prevent damage to digital phones and, later, Ethernet equipment if accidentally plugged into an analog phone jack (pair 1 disabled and 2 and 3 are used instead)
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